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</a></div> <!----></nav>  <ul class="sidebar-links"><li><a href="/fe/" aria-current="page" class="sidebar-link">大前端学习路径 + B站资源整合</a></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>HTML</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>CSS</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>JavaScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>TypeScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ES6</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue3</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="面试官-说说react-jsx转换成真实dom过程"><a href="#面试官-说说react-jsx转换成真实dom过程" class="header-anchor">#</a> 面试官：说说React Jsx转换成真实DOM过程？</h1> <p><img src="https://static.vue-js.com/1d340620-f00a-11eb-ab90-d9ae814b240d.png" alt=""></p> <h2 id="一、是什么"><a href="#一、是什么" class="header-anchor">#</a> 一、是什么</h2> <p><code>react</code>通过将组件编写的<code>JSX</code>映射到屏幕，以及组件中的状态发生了变化之后 <code>React</code>会将这些「变化」更新到屏幕上</p> <p>在前面文章了解中，<code>JSX</code>通过<code>babel</code>最终转化成<code>React.createElement</code>这种形式，例如：</p> <div class="language-jsx extra-class"><pre class="language-jsx"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
  &lt; img src=&quot;avatar.png&quot; className=&quot;profile&quot; /&gt;
  </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span><span class="token class-name">Hello</span></span> <span class="token punctuation">/&gt;</span></span><span class="token plain-text">
</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
</code></pre></div><p>会被<code>bebel</code>转化成如下：</p> <div class="language-jsx extra-class"><pre class="language-jsx"><code>React<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span>
  <span class="token string">&quot;div&quot;</span><span class="token punctuation">,</span>
  <span class="token keyword">null</span><span class="token punctuation">,</span>
  React<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span><span class="token string">&quot;img&quot;</span><span class="token punctuation">,</span> <span class="token punctuation">{</span>
    src<span class="token operator">:</span> <span class="token string">&quot;avatar.png&quot;</span><span class="token punctuation">,</span>
    className<span class="token operator">:</span> <span class="token string">&quot;profile&quot;</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">,</span>
  React<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span>Hello<span class="token punctuation">,</span> <span class="token keyword">null</span><span class="token punctuation">)</span>
<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>在转化过程中，<code>babel</code>在编译时会判断 JSX 中组件的首字母：</p> <ul><li><p>当首字母为小写时，其被认定为原生 <code>DOM</code> 标签，<code>createElement</code> 的第一个变量被编译为字符串</p></li> <li><p>当首字母为大写时，其被认定为自定义组件，createElement 的第一个变量被编译为对象</p></li></ul> <p>最终都会通过<code>RenderDOM.render(...)</code>方法进行挂载，如下：</p> <div class="language-jsx extra-class"><pre class="language-jsx"><code>ReactDOM<span class="token punctuation">.</span><span class="token function">render</span><span class="token punctuation">(</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span><span class="token class-name">App</span></span> <span class="token punctuation">/&gt;</span></span><span class="token punctuation">,</span>  document<span class="token punctuation">.</span><span class="token function">getElementById</span><span class="token punctuation">(</span><span class="token string">&quot;root&quot;</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><h2 id="二、过程"><a href="#二、过程" class="header-anchor">#</a> 二、过程</h2> <p>在<code>react</code>中，节点大致可以分成四个类别：</p> <ul><li>原生标签节点</li> <li>文本节点</li> <li>函数组件</li> <li>类组件</li></ul> <p>如下所示：</p> <div class="language-jsx extra-class"><pre class="language-jsx"><code><span class="token keyword">class</span> <span class="token class-name">ClassComponent</span> <span class="token keyword">extends</span> <span class="token class-name">Component</span> <span class="token punctuation">{</span>
  <span class="token keyword">static</span> defaultProps <span class="token operator">=</span> <span class="token punctuation">{</span>
    color<span class="token operator">:</span> <span class="token string">&quot;pink&quot;</span>
  <span class="token punctuation">}</span><span class="token punctuation">;</span>
  <span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token punctuation">(</span>
      <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>border<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
        </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>h3</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">ClassComponent</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>h3</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
        </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span> <span class="token attr-name">className</span><span class="token script language-javascript"><span class="token script-punctuation punctuation">=</span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>props<span class="token punctuation">.</span>color<span class="token punctuation">}</span></span><span class="token punctuation">&gt;</span></span><span class="token punctuation">{</span><span class="token keyword">this</span><span class="token punctuation">.</span>props<span class="token punctuation">.</span>name<span class="token punctuation">}</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span> <span class="token punctuation">&gt;</span></span><span class="token plain-text">
      </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
    <span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

<span class="token keyword">function</span> <span class="token function">FunctionComponent</span><span class="token punctuation">(</span><span class="token parameter">props</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token punctuation">(</span>
    <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>border<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
      FunctionComponent
      </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">{</span>props<span class="token punctuation">.</span>name<span class="token punctuation">}</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span> <span class="token punctuation">&gt;</span></span><span class="token plain-text">
    </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
  <span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token keyword">const</span> jsx <span class="token operator">=</span> <span class="token punctuation">(</span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">className</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>border<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token plain-text">
    </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>p</span><span class="token punctuation">&gt;</span></span><span class="token plain-text">xx</span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>p</span> <span class="token punctuation">&gt;</span></span><span class="token plain-text">
    &lt; a href=&quot; &quot;&gt;xxx&lt;/ a&gt;
    </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span><span class="token class-name">FunctionComponent</span></span> <span class="token attr-name">name</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>函数组件<span class="token punctuation">&quot;</span></span> <span class="token punctuation">/&gt;</span></span><span class="token plain-text">
    </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span><span class="token class-name">ClassComponent</span></span> <span class="token attr-name">name</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>类组件<span class="token punctuation">&quot;</span></span> <span class="token attr-name">color</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>red<span class="token punctuation">&quot;</span></span> <span class="token punctuation">/&gt;</span></span><span class="token plain-text">
  </span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre></div><p>这些类别最终都会被转化成<code>React.createElement</code>这种形式</p> <p><code>React.createElement</code>其被调用时会传⼊标签类型<code>type</code>，标签属性<code>props</code>及若干子元素<code>children</code>，作用是生成一个虚拟<code>Dom</code>对象，如下所示：</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">createElement</span><span class="token punctuation">(</span><span class="token parameter">type<span class="token punctuation">,</span> config<span class="token punctuation">,</span> <span class="token operator">...</span>children</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>config<span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">delete</span> config<span class="token punctuation">.</span>__self<span class="token punctuation">;</span>
        <span class="token keyword">delete</span> config<span class="token punctuation">.</span>__source<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token comment">// ! 源码中做了详细处理，⽐如过滤掉key、ref等</span>
    <span class="token keyword">const</span> props <span class="token operator">=</span> <span class="token punctuation">{</span>
        <span class="token operator">...</span>config<span class="token punctuation">,</span>
        children<span class="token operator">:</span> children<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token parameter">child</span> <span class="token operator">=&gt;</span>
   <span class="token keyword">typeof</span> child <span class="token operator">===</span> <span class="token string">&quot;object&quot;</span> <span class="token operator">?</span> child <span class="token operator">:</span> <span class="token function">createTextNode</span><span class="token punctuation">(</span>child<span class="token punctuation">)</span>
  <span class="token punctuation">)</span>
    <span class="token punctuation">}</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token punctuation">{</span>
        type<span class="token punctuation">,</span>
        props
    <span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">function</span> <span class="token function">createTextNode</span><span class="token punctuation">(</span><span class="token parameter">text</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token punctuation">{</span>
        type<span class="token operator">:</span> <span class="token constant">TEXT</span><span class="token punctuation">,</span>
        props<span class="token operator">:</span> <span class="token punctuation">{</span>
            children<span class="token operator">:</span> <span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">,</span>
            nodeValue<span class="token operator">:</span> text
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token punctuation">{</span>
    createElement
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre></div><p><code>createElement</code>会根据传入的节点信息进行一个判断：</p> <ul><li>如果是原生标签节点， type 是字符串，如div、span</li> <li>如果是文本节点， type就没有，这里是 TEXT</li> <li>如果是函数组件，type 是函数名</li> <li>如果是类组件，type 是类名</li></ul> <p>虚拟<code>DOM</code>会通过<code>ReactDOM.render</code>进行渲染成真实<code>DOM</code>，使用方法如下：</p> <div class="language-jsx extra-class"><pre class="language-jsx"><code>ReactDOM<span class="token punctuation">.</span><span class="token function">render</span><span class="token punctuation">(</span>element<span class="token punctuation">,</span> container<span class="token punctuation">[</span><span class="token punctuation">,</span> callback<span class="token punctuation">]</span><span class="token punctuation">)</span>
</code></pre></div><p>当首次调用时，容器节点里的所有 <code>DOM</code> 元素都会被替换，后续的调用则会使用 <code>React</code> 的 <code>diff</code>算法进行高效的更新</p> <p>如果提供了可选的回调函数<code>callback</code>，该回调将在组件被渲染或更新之后被执行</p> <p><code>render</code>大致实现方法如下：</p> <div class="language-js extra-class"><pre class="language-js"><code><span class="token keyword">function</span> <span class="token function">render</span><span class="token punctuation">(</span><span class="token parameter">vnode<span class="token punctuation">,</span> container</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">&quot;vnode&quot;</span><span class="token punctuation">,</span> vnode<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">// 虚拟DOM对象</span>
    <span class="token comment">// vnode _&gt; node</span>
    <span class="token keyword">const</span> node <span class="token operator">=</span> <span class="token function">createNode</span><span class="token punctuation">(</span>vnode<span class="token punctuation">,</span> container<span class="token punctuation">)</span><span class="token punctuation">;</span>
    container<span class="token punctuation">.</span><span class="token function">appendChild</span><span class="token punctuation">(</span>node<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// 创建真实DOM节点</span>
<span class="token keyword">function</span> <span class="token function">createNode</span><span class="token punctuation">(</span><span class="token parameter">vnode<span class="token punctuation">,</span> parentNode</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">let</span> node <span class="token operator">=</span> <span class="token keyword">null</span><span class="token punctuation">;</span>
    <span class="token keyword">const</span> <span class="token punctuation">{</span>type<span class="token punctuation">,</span> props<span class="token punctuation">}</span> <span class="token operator">=</span> vnode<span class="token punctuation">;</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>type <span class="token operator">===</span> <span class="token constant">TEXT</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        node <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createTextNode</span><span class="token punctuation">(</span><span class="token string">&quot;&quot;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> type <span class="token operator">===</span> <span class="token string">&quot;string&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        node <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createElement</span><span class="token punctuation">(</span>type<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> type <span class="token operator">===</span> <span class="token string">&quot;function&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        node <span class="token operator">=</span> type<span class="token punctuation">.</span>isReactComponent
            <span class="token operator">?</span> <span class="token function">updateClassComponent</span><span class="token punctuation">(</span>vnode<span class="token punctuation">,</span> parentNode<span class="token punctuation">)</span>
        <span class="token operator">:</span> <span class="token function">updateFunctionComponent</span><span class="token punctuation">(</span>vnode<span class="token punctuation">,</span> parentNode<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
        node <span class="token operator">=</span> document<span class="token punctuation">.</span><span class="token function">createDocumentFragment</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token function">reconcileChildren</span><span class="token punctuation">(</span>props<span class="token punctuation">.</span>children<span class="token punctuation">,</span> node<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">updateNode</span><span class="token punctuation">(</span>node<span class="token punctuation">,</span> props<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> node<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// 遍历下子vnode，然后把子vnode-&gt;真实DOM节点，再插入父node中</span>
<span class="token keyword">function</span> <span class="token function">reconcileChildren</span><span class="token punctuation">(</span><span class="token parameter">children<span class="token punctuation">,</span> node</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> children<span class="token punctuation">.</span>length<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">let</span> child <span class="token operator">=</span> children<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>child<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">let</span> j <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> j <span class="token operator">&lt;</span> child<span class="token punctuation">.</span>length<span class="token punctuation">;</span> j<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
                <span class="token function">render</span><span class="token punctuation">(</span>child<span class="token punctuation">[</span>j<span class="token punctuation">]</span><span class="token punctuation">,</span> node<span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
            <span class="token function">render</span><span class="token punctuation">(</span>child<span class="token punctuation">,</span> node<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token keyword">function</span> <span class="token function">updateNode</span><span class="token punctuation">(</span><span class="token parameter">node<span class="token punctuation">,</span> nextVal</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    Object<span class="token punctuation">.</span><span class="token function">keys</span><span class="token punctuation">(</span>nextVal<span class="token punctuation">)</span>
        <span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span><span class="token parameter">k</span> <span class="token operator">=&gt;</span> k <span class="token operator">!==</span> <span class="token string">&quot;children&quot;</span><span class="token punctuation">)</span>
        <span class="token punctuation">.</span><span class="token function">forEach</span><span class="token punctuation">(</span><span class="token parameter">k</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>k<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">)</span> <span class="token operator">===</span> <span class="token string">&quot;on&quot;</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token keyword">let</span> eventName <span class="token operator">=</span> k<span class="token punctuation">.</span><span class="token function">slice</span><span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">toLocaleLowerCase</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            node<span class="token punctuation">.</span><span class="token function">addEventListener</span><span class="token punctuation">(</span>eventName<span class="token punctuation">,</span> nextVal<span class="token punctuation">[</span>k<span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
            node<span class="token punctuation">[</span>k<span class="token punctuation">]</span> <span class="token operator">=</span> nextVal<span class="token punctuation">[</span>k<span class="token punctuation">]</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// 返回真实dom节点</span>
<span class="token comment">// 执行函数</span>
<span class="token keyword">function</span> <span class="token function">updateFunctionComponent</span><span class="token punctuation">(</span><span class="token parameter">vnode<span class="token punctuation">,</span> parentNode</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">const</span> <span class="token punctuation">{</span>type<span class="token punctuation">,</span> props<span class="token punctuation">}</span> <span class="token operator">=</span> vnode<span class="token punctuation">;</span>
    <span class="token keyword">let</span> vvnode <span class="token operator">=</span> <span class="token function">type</span><span class="token punctuation">(</span>props<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">const</span> node <span class="token operator">=</span> <span class="token function">createNode</span><span class="token punctuation">(</span>vvnode<span class="token punctuation">,</span> parentNode<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> node<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token comment">// 返回真实dom节点</span>
<span class="token comment">// 先实例化，再执行render函数</span>
<span class="token keyword">function</span> <span class="token function">updateClassComponent</span><span class="token punctuation">(</span><span class="token parameter">vnode<span class="token punctuation">,</span> parentNode</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">const</span> <span class="token punctuation">{</span>type<span class="token punctuation">,</span> props<span class="token punctuation">}</span> <span class="token operator">=</span> vnode<span class="token punctuation">;</span>
    <span class="token keyword">let</span> cmp <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">type</span><span class="token punctuation">(</span>props<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">const</span> vvnode <span class="token operator">=</span> cmp<span class="token punctuation">.</span><span class="token function">render</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">const</span> node <span class="token operator">=</span> <span class="token function">createNode</span><span class="token punctuation">(</span>vvnode<span class="token punctuation">,</span> parentNode<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">return</span> node<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">export</span> <span class="token keyword">default</span> <span class="token punctuation">{</span>
    render
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre></div><h2 id="三、总结"><a href="#三、总结" class="header-anchor">#</a> 三、总结</h2> <p>在<code>react</code>源码中，虚拟<code>Dom</code>转化成真实<code>Dom</code>整体流程如下图所示：</p> <p><img src="https://static.vue-js.com/28824fa0-f00a-11eb-ab90-d9ae814b240d.png" alt=""></p> <p>其渲染流程如下所示：</p> <ul><li>使用React.createElement或JSX编写React组件，实际上所有的 JSX 代码最后都会转换成React.createElement(...) ，Babel帮助我们完成了这个转换的过程。</li> <li>createElement函数对key和ref等特殊的props进行处理，并获取defaultProps对默认props进行赋值，并且对传入的孩子节点进行处理，最终构造成一个虚拟DOM对象</li> <li>ReactDOM.render将生成好的虚拟DOM渲染到指定容器上，其中采用了批处理、事务等机制并且对特定浏览器进行了性能优化，最终转换为真实DOM</li></ul> <h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li>https://bbs.huaweicloud.com/blogs/265503)</li> <li>https://huang-qing.github.io/react/2019/05/29/React-VirDom/</li> <li>https://segmentfault.com/a/1190000018891454</li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <!----> </main></div><div class="global-ui"><!----></div></div>
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